Area Forecast Discussion
Issued by NWS Louisville, KY
Issued by NWS Louisville, KY
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909 FXUS63 KLMK 010713 AFDLMK Area Forecast Discussion National Weather Service Louisville KY 313 AM EDT Wed May 1 2024 .KEY MESSAGES... * Dry and warm today and Thursday with highs in the 80s. A few locations could touch 90 degrees Thursday. * Widespread showers and scattered thunderstorms on Friday, with brief heavy rain and lightning. * Rain chances linger into Saturday, but forecast confidence remains low at this time. && .SHORT TERM /THROUGH TONIGHT/... Issued at 312 AM EDT Wed May 1 2024 The weather is quiet early this morning with very light to calm winds and partly cloudy to mostly clear skies. Separate areas of convection continue in portions of IL and MO/OK, but we will only see thin cirrus spread overhead from the west. Temperatures range through the 50s, except in Louisville`s urban heat island. Fog development has been limited thus far and confined to eastern KY. However, we are now seeing valley fog develop in the Bluegrass and Lake Cumberland regions. Will keep an eye on those eastern counties - may need to consider a SPS for patchy dense fog south of the BG Parkway and perhaps east of a Glasgow to Lawrenceburg line. The low pressure system currently over the Upper Midwest will continue to lift northeast today across Lake Superior and southern ON. Meanwhile, upper level ridging will gradually amplify over the Southeast and Ohio Valley. The northern stream wave`s weakening cold front will sink toward the Lower Ohio Valley this evening. Southwesterly sfc winds will increase to 5-10 mph today to the south of the sfc boundary. Moisture does pool along the boundary, with precipitable water rising to 1.0-1.2 inches. HREF mean SBCAPE is around 1500 J/kg around 21-00Z across southern IN and portions of central KY. However, lift provided by the increasingly diffuse sfc boundary is very weak. Most CAMs suggest little to no convection, so will cap PoPs around 10%. Expect a cumulus field to develop for the second half of the day, along with continued thin cirrus floating overhead. Overall, a nice warm Spring day with afternoon highs in the low to mid 80s. A sfc ridge of high pressure will extend along the Appalachians tonight, and we`ll see diminished cloud cover and light southeasterly flow. Expect a mild, quiet night with lows in the upper 50s to lower 60s. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Issued at 312 AM EDT Wed May 1 2024 ========== Long Term Overview ========== Low-amplitude western trof/eastern ridge pattern aloft on Thursday will further flatten out heading into the weekend. Progressive zonal flow tends to feature disturbances that are difficult to time, so forecast confidence is limited especially over the weekend. High confidence in hot temperatures (by early May standards) on Thursday and rain on Friday, with much lower confidence regarding rain chances on Saturday. Unsettled weather pattern continues Sunday into the first half of next week. Look for daily rain chances and temps above normal for this time of year. ========== Heat Potential for Thursday ========== Unseasonably warm temps are expected on Thursday with deep southerly flow, but the question is just how hot we get and how much of a player the humidity will become. Look for temps at least in the mid/upper 80s throughout central Kentucky and southern Indiana, and some locations could still easily touch 90F given that roughly half the NBM ensemble members show highs AOA 90, especially for the urban heat islands. Dewpoints in the upper 50s or lower 60s will not push heat indices above the actual temp, but will be just enough to feel "muggy." Experimental HeatRisk for the 24-hr period still shows minor impacts, but the max temps are solidly into the territory where a large, vulnerable outdoor population would be impacted. If you`re planning to spend substantial time outdoors on Thursday, be sure to practice heat safety be staying properly hydrated and taking breaks indoors if possible. ========== Thunder Potential for Friday ========== Widespread showers and a few thunderstorms are expected on Friday as an upper wave lifts ENE into the Great Lakes and pushes a weak cold front into the Ohio Valley. Plenty of moisture available and enough instability to support scattered thunderstorms, the wind fields are too weak to support severe convection. Rainfall rates could be briefly heavy, but it`s not a continuous, all-day rain. The rain chance for the day is roughly 80 percent, but thunder chances will peak around 40 percent in the late afternoon and evening. Cold front is expected to pass through Friday night or early Saturday morning, resulting in lower PoPs as we get into the weekend. Confidence in the details beyond Friday night is low, as it depends on where the front hangs up. ========== Uncertainty for Saturday ========== Ensemble forecasts continue to be a crapshoot with roughly half the ensemble members still kicking out measurable precip near Louisville, with higher POPs to the south and east and lower POPs to the west and northwest. The operational GFS and ECMWF are in surprisingly good agreement in hanging the front up between Louisville and Bowling Green, and trying to wave it back to the north later on Saturday. Given the subtle nature of the upper wave forcing it, will take this solution with a grain of salt and stay close to the NBM for now. That will run our precip chances near 40% anytime Saturday, with about a 20% chance for thunder. It may take a few forecast cycles before this comes into any clearer focus, so stay tuned. && .AVIATION /06Z TAFS THROUGH 12Z THURSDAY/... Issued at 137 AM EDT Wed May 1 2024 VFR conditions will prevail through much of the period. Fog will likely impact visibility briefly this morning at RGA, but confidence in any impacts from fog is much lower at the other terminals. RGA is most likely to see IFR/LIFR vis in dense fog through sunrise. LEX may see some brief vis reductions after 08Z, most likely in the MVFR range. Cannot rule out brief IFR, however. SDF/BWG/HNB appear likely to remain VFR. Calm to very light southerly winds are expected through sunrise, with winds veering southwesterly and increasing to 5-10 mph by late morning. A SCT cu field will take shape across southern IN and the northern half of central KY late this afternoon and evening as moisture pools along a weak cold front. There is a 10% chance for an isolated shower/storm near HNB after 20Z. Otherwise, dry weather will continue. && .LMK WATCHES/WARNINGS/ADVISORIES... KY...None. IN...None. && $$ SHORT TERM...EBW LONG TERM...RAS AVIATION...EBW